Bending of corkwood



March 23,1948. LAK 2,438,349

BENDING OF CORKWOOD Filed April 28, 1944 2 Sheets-Sheet 1 INVEN TOR. Frederic/E 7 P022611:

A T 70 R N E Y March 23, 1948. F. F. POLLAK 2,438,349

BENDING OF CORKWOOD Filed April 28, 1944 2 Sheets-Sheet 2 INVENTOR. Frederick F oZZak Y ATTORNEY if subjected ,ing members of Patented Mar. 23, 1948 UNITED TATiEiS ,BENDING F CORKWGOD -Frederick F. :Pollak, New York N. ZY. Application April 28, 1944,,Serial No. 533,219 Claims. (01. 144- 309) This invention relates to important ,developments of the methods forthetreatment ofvcorkwood, balsawood and similar light :WOOdSdlS- closed in my c-opendingpatent application Ser. No. 527,505.

This application is based on ,the recognition that corkwood and particularly its lightestrepresentative, the bals awood, undergoes a remark.-

able and astonishing alteration of its properties,

:to certain comparatively ,simple and particularly to compression,

, the structure and 1 the textreatments swelling and dryin ture of the :wood isthereby entirely changed; the

previously fragile and easily breakablewo-odlis in this manner converted into a material which is Well usable for -many purposes and particularly also as a constructional and building material.

The present invention is an important supplement in thisrespect and it is-the mainobjectto bend 'corkwood; and ;balsawo od into desired arcuated shapes.

It is also an object of the invention to produce uniformly and symmetrically bent balsawood workpieces and to avoid irregularities ofthefinal form.

It is a particular object of the invention to produce :from corkwood and balsawood perfect circular and'part-circular articles.

'11; is alsoan object ofthe invention {to combine with the bending of the Wood treatmentswhich improve its properties and particularly increase its strength. and hardness.

It isa further object of the-invention to establish the principles which permit the creation-of faultless bends and, therefore, assure the pro- -duction of highly usable bent corkwood find balsawood articles.

Further objects and will be apparent from in conjunction with the purposes of my invention the following description attached drawing of which in anintermediary and inthe'flnal stage of the bending operation,

As .generally known, the shaping of wood,.by

bonding is a;rat her difficultproblem. .In order to bend wood into curved andarcuated bodies, for

instance, into circular or part-circular articles, the dried but otherwise mechanically ,untreated Wood ,is subjected to the individual or the 0031- ones'ide from their PATENT orFicE bined action of heat,.steam and pressu e; a certain bending action may also she imparted to wood by mere pressure and without the applicatiori ofheatorstealn.

This situation, however, is entirely ,diverse in the case of corkwoo'd and 'balsawojod; thesetypes of light woodc'annot be bent-to anyappreciable degree in their original state; 'onlyby a .compound with veneersland due to the support created thereby a limited bending of ,corkwood and balsawood may be accomplished.

jllhe non-bendability is caused by the peculiar structure and texture of thesellght wood types.

As explained in my "former application the oorkwood and particularly the;ba1sawood may wellvbe identified as an extremelyunyieldable and stiff agglomeration of hollow longitudinally orientated comparatively short fibers, similar in their characteristics to short straw halms which are united by transversebandathe intersticeslbetween the hollow-fibers being partly filled with incrustation masses.

If balsawood is compressed by pressure acting vertically to the longitudinal direction of the hollow fibers, thetransverse structure. supporting elements are disrupted and probably freed on the compound with the longitudithe. union on the other side when the compressed balsawood is swelled up by imbib'ition, the transverse supports seemto assume their former location and to impart "to the mainfibers asupport-whlch is similar to the ,one'which vexisted m thetinitial state; the swelled up bodiesdo not :materially change; their shape by drying.

Th s as ob erv tio i e liz d amend n i the instant invention for bending-halsawoodland the previously made statement that balsavvoo'd cannot be bent toanysappreciable degree is now suplemented insofaras, a'lbending againstthedirection of the .Ifibersis entlrelyjimpossible; even r al fibers, whereas remains unaltered;

the slightest attempt in this r spe t is, bound to .be va -faih 1re, .sincethe iiloers are utterly fragile n a m a el u tured'ala brqken 'ih' least ,be ding .stress is imparted thereto; slight arcuat efrmatiq ar an nnae i h th aters- Furthermore, it must be kept'in mindgthat-the bending ,of a bodyinvolves an elongati-on' of its outside layersanda compression ofthelayers which are located at its inside. -The displacem nt the e t q e ieiww v ou fi e Pl c eeee enee l i re e ibe l center tion. of its original volume the bent pieces retain -ized that another .to bendability,

compressed, the

imparted thereto after allbeing a the magnitude of this greatly influences the by compressing the wood to about one-fifth to one-tenth of its initial thickness and reswelling the same through imbibition with boiling water to about 50 to 90% thereby increased and a bending at least to a limited extent was rendered possible.

Further experimentation, however, proved that y the thus produced bendings were irregular and that, for instance, satisfactory circular or partcircula'r workpieces could not beobtained.

I realized that sufficient softness and pliability might not be the only influencing. factor in the art of bending balsawood and that the displacementof each individual particle of the softened balsawood and the length of the way might have to be considered which each particle must travel during the bending operation.

l Furthermore, I conceived that the extent of this displacement would be directly related to the thickness of thebalsawood workpieces. If, for instance, two boards of a different thickness are bent into circular and part-circular bodies, the incurvation at. the circumference of the thicker 'body will be larger and every particleof this body must travel a longer way during the bending operation; it thus became apparent that in addition to the softness of the balsawood the thicknessof the workpieces influences the bendability; as anatural consequence of this mental analysis the advisability arose to subject the balsawood to high compression and to reducto thin pieces before subjecting thesame to further treatment.

In the practical realisation of this principle it was found that balsawood sheets upon compression by a high pressure of about 2000 lbs/sq. inch to inch from about times their original thickness could be comparatively easily bent by means of a suitable mold. If the bent objects are then immersed in water, swelled-up and dried in the mold at a temperature of about 110 0.,

their shape even when reimmersed in water. w

In order to produce thicker articles several bent bodies weresuperposed, glued and pressed together. This method, however, resulted in a breakage of the bent pieces.

Only at this state of my investigations I realpeculiar property of the balsawood might have tobe considered with regard and this is the remarkable inertness of the particles of the compressed wood and their indisposition to move. If balsawood is fibers remain in the location :by the compression, whereas wood product, it could be ex-' pected that the fibers would resume their former position and shape as soon as the pressure was released.

This observation led to the necessity to perform the bending of the compressed balsawood in such a manner that sufiicient time was given to the particles to overcome their natural inertness and to move under the influence of the of its original thickness. The softness and pliability of the balsawood is '3. The bendin themselves in bending force into new positions; in other words) the necessity arose to bend slowly.

The above recited various observations resulted in the establishment of certain principles with regard to the successful bending of cork- .wood and balsawood, which are summarized as follows:

1. Cork and balsawood must be strongly compressed and reduced in thickness before the bending is commenced;

2. If sufficiently compressed, the wood can be bent by means of a suitable mold irrespective of its initial thickness, if certain additional precautions are observed;

rate which permits its particles to establish the new location resulting from in other words, the bending must aslow rate;

the bending; be performed at 4. The bent redried in the bending mould.

During my endeavors to produce bodies of greater thickness by uniting strongly compressed bent parts, an observation was made of particularly interesting nature.

Three semi-circularly bent thin pieces were superposed upon each other and located in water for reswelling purposes. A small weight was placed on top of the combined body. A lifting ofthe weight was expected to take place equally to the increase of thickness caused by the reswelling of the three pieces.

. However, the weight rose culated height. V V 7 Upon examination of this rather surprising result it was found that the uppermost of the three semi-circular objects had greatly changed its circular form in its center portion and the latter had assumed a somewhat pointed rectangular shape, whereas far above the precalthe two side portions of the same had preserved the circular form. It

was o'bvious that the distortion gof the center portion had caused the increase in height over the expected ratio. r a a The lowermost of the three pieces, however, had retained its regular semicircular shape; the center portion of the middle piece showed a change of form lying between theistrong deformation of the uppermost pieceandthesh'ape preservation of the lowermost piece.

The peculiar action and the strong' distortion of the uppermost piece was obviously caused by the great swelling pressure exerted upon the same from theoutside. a H

Similar distortions of semi-circular bent pieces were ascertained, when thicker pieces were located for swelling in bending moldsythe working surfaces of which had a' small radius and an accordingly great incurvation. 1

When semi-circular bending molds'of this type were used for the swelling of the bent pieces, foldlike irregularities 'and'breakages occurred in the center portion of the treated workpieces. 7

From these observations it appeared that a definite relation exists between the thickness of the compressed balsawood and the extent 'ofincurvation up towhich it may be safely bent, and that this bending limit is controlled by the smallest admissible radius of the curv'eor circle imparted .to the compressed balsawoodj in fothe'r words, the. art of bending balsawood "articlesby compression and reswelling was seemingly governed by a certain direct relation between arnaximum thickness of the compressed workpieces and a minimum bending radius" which is the ramust be performed at a timely material must be reswelled and a l aeesgeee dius of; the inner final, incurvation" imparted to breakages will result.

Needless to point out that balsawoodworkpieces, which in, the light ofth'e'aboveexplained theory hadbeen improperlytreat'ed would" have a weak spot in their-center portion and; therefore be not usable for most purposes'and' particularly not for ccnstructional'workand fOlfbllil'd ing and similar purposes;

Based on the above explained principles and purposes of this invention the bending ofbalsa wood will now be described in. detailwith reference to theaccompanyingitdrawin'gz A rectangularb'oard' 4 was cut from air dried balsawood; due.toits:sof.tness the'wood can be easily cut into desired shapes by means of ordinary cutting or similar tools.

The board is charged between the plane platens-of a customary, forinstance. hydraulic press and compressed at room or a slightly elevated temperature for a period of several minutes at a pressure which may be advantageously maintained between 1000 and 3000 lbs/sq. inch or more.

The board is thereby-compressed up to about 1% of its original thickness without otherwise undergoing a change of its shape; the compressing conditions will vary with the size of the workpieces and the degree of compression.

The equipment used for bending the compressed balsawood board 4 is composed of a lower tubular circular mold member I made of a sufficiently hard material, such as steel.

This mold member I is provided with two series of bores 8 adjacent to its lower two edges. Threaded bolts 3 are located in these bores; the bolts carry at their upper ends a thin plate 2 of a fitexilble strong material, for instance flexible s cc The bending mold is situated i a vessel 5 provided with a feed pipe 6 and a discharge pipe 7.

The compressed balsawood board 4 is placed between the two members i, 2 of the bending mold, as shown in Fig. 1.

The bolts are gradually tightened by screws 9 and plate 2 is thereby slowly forced into an incurvation; as soon as the plate 2 reaches the board, the latter is bent. The tightening is continued until a distance is reached between the upper and the lower mold members which corresponds to about between 6 to 9 tenths of the thickness of the original board. At this phase of the bending operation the board has been forced into a shape approximately resembling the one shown in Fig. 3, which figure illustrates the second stage of the work.

The previously stated rule must be observed to perform the bending carefully and slowly, as the balsawood particles require a certain time to travel into their new locations in conformity with the gradually changed shape of the board,

Water is now admitted to vessel 5 through tube 6 and the board swells by imbibition; under the influence of the pressure resulting from the swelling the bending of the board continues until it tightly contacts on its outside the mold members I, 2, assuming at the same time the shape shown in Fig. 4, which shape is identical to the space between the two mold members.

The end shaping by swelling requires approximately minutes, if the initial thickness of the board is about one inch.

It is to be noted that this end shaping is mainly accomplished by the pressures resulting front tlfe swelling of the wood which-fea most desirable working condition. v

The mold maybe provided witlrsuitable heating means which will render it'po'ssible to carry out the work at an elevatedtemperature.

As soon as the;final bendinghasbeen accoinplished by reswelling between the two moldimemgbers I, 2, the water is discharged 'from vesse '5 the board including the mold 'is now-located suitable drying oven where itismain'taine'd at a temperature of IUD- 200 G; untirthewood-isprae tically dry.

Hereupon the bent board is rem-overflow the bending apparatus by unscrew iirg tlie bblt's'. it now represents the finished arti'cl Instead of swellingtheb'ent artiele by imbibition with water solutions may 'be used i'mpartiiig to the woodspecifiedesired propertiesy'for dnstance, strength andliardhe'ss';

The bent board'may also be impregnatedinthe manner disclosed in my former application; 'Ser. N 0. 527,505, with solutions of't-hermosettiirgresins and hardened to transform the -sol-ub-le-resiii into its final insoluble state; it may'be advantageous to raise the drying temperature in order to-aocelerate the process; in this way it is:possible to produce in one operation hardened bent pieces of balsawood.

The bending operation ma be combined in this manner with the introduction of disinfecting, sterilizing, mildew and pest proof substances, coloring agents or products which may'impart to the wood one or more specific properties.

Any liquid may be used for this purpose provided that it is not repulsed by the wood; it is advisable to use solutions of the impregnating materials in liquids which easily penetrate into the wood. If, for instance, it is intended to impregnate the wood with an oily substance, such as linseed or tung oil, the oils are dissolved in liquids, for instance alcohol, ether or acetone, and incorporated into the compressed wood with or without the addition of hardeners or other substances which are soluble in the solvent. The bending operation is in no way changed or influenced by the impregnation; only the drying may be varied in accordance with the special character of the substances or solutions used.

The invention is described in this specification by way of example only, and it is fully understood that changes and deviations thereof may be made in accordance with individual requirements within the scope of the appended claims.

I claim:

1. Method for the manufacture of a curved workpiece from corkwood comprising compressing a sheet thereof, slowly bending same to curved formation short of its final curved shape, con fining said bent sheet between spaced shape-confining faces having the desired curved shape of the finished article and while so confined, im- :bibing said sheet, resw-elling same to occupy the space between said faces, to form a curved workpiece and drying the thus produced curved workpiece while maintaining the same between said space confining faces.

2. Method for the manufacture of a curved workpiece from corkwood comprising compressing a sheet thereof to about one fifth to one tenth of its original thickness, slowly bending same to curved formation short of its final curved shape, confining said bent sheet between spaced shapeconfining faces having the desired curved shape of the finished article and while so confined, im

.the space between said faces to form bibing said sheet, reswelling same to occupy the space between said faces, to form-a curved workpiece and drying the thus producedcurved workpiece while maintaining the same between said spaceconfining faces. v .c i

3. Method for the manufacture of a curved workpiece from corkwood comprising compressing a sheet thereof, slowly bending same to curved formation short of its final curved shape,'confining said bent sheet between spaced shape=con fining faceshaving the desired curved shape of the finished article and while so confined imbibing said sheet with an aqueous solution of thermosettting resinsQreswelling same to occupy the space between said faces, to form a curved workpiece and drying the thus produced curved workpiece while maintaining the same between said space confining faces. I

4. Method for the manufacture of a curved workpiece from corkwood comprising compressing a sheet thereof, slowly bending same to curved formation short of its final curved shape, confining said bent sheet between spaced shape-confining faces having the desired curved shape of the finished article and while so confined imbibing said sheet with an aqueous solution of sterilizing substances, reswelling same to occupy a'cur-ved workpiece and drying the thus produced curved workpiece while maintaining the same between said space confining faces. v i

' 5. Method for the manufacture of a, curved workpiece from corkwood comprising compressing a sheet thereof; slowly bending same to curved formation short of its final curved shape, confining said bent sheet between spaced shape-confining faces having the desired curved shape of the finished article and while so confined, imbibing said sheet with an aqueous solution of thermosetting resins-and reswelling same to occupy the space between said faces, to form a curved workpiece, drying the thus produced curved workpiece and hardening the same at atemperatureof between about to C. while maintaining the same between said space confining faces.

FREDERICK F. POLLAK.

' REFERENCES CITED 7 The following references are of record in the file of this patent:

UNITED STATES PATENTS' 

